The present invention relates generally to a spark ignition engine and, more particularly, to a spark ignition engine capable of fixing an ignition coil case even in a small engine.
In some spark ignition engines, conventionally, a cylinder head cover is attached to a top surface of a cylinder head, a plug hole is formed on the top surface of the cylinder head at an outside of the cylinder head cover, a spark plug is fixed to an inner part of the plug hole, an ignition coil integral type plug cap is attached to the spark plug, the plug cap being formed by attaching a flexible cylinder portion to an ignition coil case, and a tip part of the flexible cylinder portion is inserted into the plug hole and is thus fitted in the spark plug (for example, see Japanese Unexamined Patent Publication No. 2010-255621 (FIG. 3)).
According to the engine of this type, it is possible to obtain an advantage that a distance from the ignition coil to the spark plug is reduced to minimize a voltage loss.
In the conventional technique, however, an attachment flange is fixed to the top surface of the cylinder head, a hole extension cylinder is formed on the attachment flange, the hole extension cylinder is caused to communicate with the plug hole, and the flexible cylinder portion is inserted into the plug hole through the hole extension cylinder so that the ignition coil case is fixed to the hole extension cylinder, which causes a problem.
In the small engine, the ignition coil case cannot be fixed. The attachment flange is fixed to the top surface of the cylinder head, the hole extension cylinder is formed on the attachment flange, the hole extension cylinder is caused to communicate with the plug hole, the flexible cylinder portion is inserted into the plug hole through the hole extension cylinder and the ignition coil case is fixed to the hole extension cylinder. Therefore it is necessary to fix the attachment flange to the top surface of the cylinder head. And in the small engine in which the cylinder head has no such space, the ignition coil case cannot be fixed.